1. Field of the Invention
The present invention relates to a thin film transistor in which a channel region is formed of a crystallized SiGe film and a manufacturing method thereof.
2. Description of the Related Art
A thin film transistor (TFT) made of polycrystalline silicon (Si) can be easily formed on a substrate such as a glass or the like by some suitable means such as the irradiation of laser beams, the heating using an electric heating furnace or the like after an amorphous silicon film was formed by a chemical vapor deposition (CVD) or the like. The thin film transistor made of polycrystalline silicon has a carrier mobility of 50 to 100 (cm.sup.2 /Volt.multidot.Second) which is extremely small and about 1/6 of that of a thin film transistor made of single crystal silicon. Therefore, a high speed circuit whose switching speed is higher than 10 MHz cannot be manufactured by using such polycrystalline silicon thin film transistor.
To remove the aforesaid shortcomings, there are proposed a wide variety of techniques such as to increase a carrier mobility of a thin film transistor by increasing a grain size of active region formed of polycrystalline silicon film, for example.
A technique in which a semiconductor thin film such as a an amorphous silicon hydride (a-Si:H), an amorphous germanium hydride (a-Ge:H) or the like is melted and crystallized by the irradiation of pulse laser beams in a variety of semiconductor integrated circuits receives remarkable attention as a technique that can manufacture thin film transistors having large carrier mobility at low temperature. Various researches have hitherto been made in order to establish a technique in which thin film transistors can be manufactured at low temperature according to the pulse anneal treatment.